Graphing with higher-order procedures

Relevant section in text: 1.3

The assignment develops a representation of points in the plane as
procedures that take 0 or 1 as an argument and returns,
correspondingly, an x or y coordinate. (This is precisely the
procedural representation of pairs described in section 2.1.3.)
Starting with this, students build a functional language of curves and
transformations on curves, including a recursive transformation that
draws fractal curves.

This assignment can be a bit mindblowing, since it gives such a fast
immersion into higher-order procedures.